The invention is directed generally to internal combustion engines and more particularly to those engines that employ hydraulic valve lifters for valve lifter operation which require a source of oil to be delivered under pressure thereto. Hydraulic valve lifters are well known the engine art and, therefore, will not be discussed in any great detail herein.
In state of the art engines employing hydraulic valve lifters, oil under pressure is supplied to the lifters from the engine oil pump. For new engines and engines with fresh oil this means for supplying oil the hydraulic lifters is generally satisfactory for average engine operation. However, when the oil gets old, or extremely hot or the engine begins to wear the normal oil pressure supplied from a conventional engine oil pump drops in pressure. This drop in pressure reduces flow of oil and the pressure of that oil delivered to the lifters resulting in less lifter movement and/or the hydraulic lifter plunger loosing contact with the valve stems at certain engine RPM resulting in a change in the normally expected valve timing at various speeds.
Generally the function of the hydraulic lifter is to maintain physical contact between the valve drive link(s), ie. between the cam lobes and valve stems or rocker ends to reduce valve actuation mechanical noise and to continually make adjustments for gear and valve link wear while maintaining that physical contact. No consideration is given to change or intentional modifying valve lifter operation to overcome inaccurate valve timing at various RPM where slight valve stem length adjustment is necessary to cause slightly different valve timing and lift for ideal operation engine operation at different RPMs.
Other methods of variable valve timing include advance and retard systems, multi-profile cams, solenoid/helenoid actuated valves, and high leak hydraulic lifters.
The present invention fills a long felt need for a valve lifter system that compensates for engine wear and the resulting low oil pressure delivered to the valve lifters and the need to control the degree of lift of the valves through the lifters during valve opening and closing at different engine RPM.